1. Field of the Invention
The embodiments presented herein relate to detecting a blockage or a void on the aperture of an image sensor.
2. Description of the Related Technology
Image sensors are components mounted on the belt transport plate of sorting machines. In one embodiment, the sorting machines are configured to receive mail items. In one non-limiting embodiment, these image sensors are used in postal operations to capture images of the front or back side of the mail and to process the images in order to detect and decode the information printed on the mail piece for mail processing automation. In certain embodiments, these images are barcodes. Optical Character Reading is one additional function that can be implemented on such image sensors.
With letter and flat mail sorters, the mail travels in front of the image sensor and in close proximity with the face plate of the image sensor head and with the sapphire window (aperture) of the sensor. The image sensor scans the item one column of the item at a time from one end or edge of the item to the other.
One of the most common causes of failure in such devices is foreign matter that becomes attached to the outer side of the aperture window. Such foreign matter prevents the light of the image sensor light source from reaching the target mail piece and blocks the light reflected by the target mail piece from reaching the image sensor. Most often, foreign matter can be dust or debris in various amounts, glue mixed with dust or pieces of paper of different sizes including paper labels with adhesive backing, frequently used in mail preparation and processing. If the image sensor aperture is blocked and the image cannot be scanned in a way that the rest of the system can continue processing the item, there is generally no way to timely tell that there is a problem with image sensor aperture.
Typically, this kind of blockage may occur when a mailing label or barcode label or some other type of label or sticker which is affixed to the item dislodges, gets separated from the envelope and sticks to the aperture, partially or totally blocking the aperture. When this happens, the image sensor does not get a complete image of the item. However, because the system is moving at such a high speed and the volume of items passed in front of the aperture is so large, hundreds or even thousands of pieces of mail therefore pass through the system before it is realized that there is a problem. Further, all of the items that passed in front of the image sensor likely need to be reprocessed due to the fact that the image sensor that is reading the information has a blocked aperture.